The present invention relates to a method of manufacturing a semiconductor device. More particularly, the invention relates to a semiconductor masking device which can completely flatten a level difference portion of an insulating film formed due to irregularity on a semiconductor substrate, a method of manufacturing the semiconductor masking device and a method of manufacturing a semiconductor device using the semiconductor masking device.
As a semiconductor device has achieved a higher density and has become more refined, a technique to flatten the surface of an insulating film has become more and more significant.
A conventional method of manufacturing a semiconductor device having a multilayer interconnection structure will now be described referring to FIGS. 13(a) through 13(e).
As is shown in FIG. 13(a), interconnections 91 are first formed on a semiconductor substrate 90 bearing semiconductor elements, and then, as is shown in FIG. 13(b), an interlayer insulating film 92 of, for example, a silicon oxide film is deposited on the semiconductor substrate 90 so as to cover the interconnections 91.
Next, as is shown in FIG. 13(c), in order to flatten the surface of the interlayer insulating film 92, a resist film 93 is formed by coating the interlayer insulating film 92 with a flattening material such as a resist.
Then, as is shown in FIG. 13(d), the resist film 93 is etched as a first etch back process. In this etch back process, an end point detector is generally used so as to stop the etching when the surface of the interlayer insulating film 92 is exposed. After this, as is shown in FIG. 13(e), a second etch back process is conducted under conditions which make the etching rate for the interlayer insulating film 92 equal to that for the resist film 93, so as to flatten the surface of the interlayer insulating film 92.
In the case where the surface of the interlayer insulating film is flattened in the aforementioned manner, however, when a distance between the adjacent interconnections 91 causing level differences underneath is several .mu.m or more, the surface of the interlayer insulating film 92 has recesses after completing the etching because of the coating characteristic of the resist film 93. Since the etch back is a technique to transfer the flatness of the top surface of the resist film 93 to the surface of the interlayer insulating film 92 as the ultimate surface form, the surface of the interlayer insulating film 92 ultimately obtained has the recesses.
In this manner, in the conventional method of manufacturing a semiconductor device, it is impossible to decrease an absolute level difference formed on the surface of the interlayer insulating film 92.
Furthermore, as a semiconductor element has been more refined, it is also significant to secure a depth of focus in lithography. In the aforementioned conventional method of manufacturing a semiconductor device, however, since the absolute level difference formed on the surface of the interlayer insulating film cannot be decreased, the depth of focus cannot be improved. This automatically leads to a limit in the refinement of a semiconductor element.
In order to solve the aforementioned problems, it is indispensable to introduce a technique to completely flatten an interlayer insulating film, and chemical mechanical polishing has recently attracted attention as the completely flattening technique for an interlayer insulating film. However, the flattening of an interlayer insulating film by the chemical mechanical polishing has various problems as follows: (1) It is necessary to introduce new equipment; and (2) the polishing process has obvious pattern dependency and is very difficult to control.